N. R. Taskar

On the Mechanism of Growth of CdTe by Organometallic Vapor‐Phase Epitaxy

In this paper are presented some experimental results to explain mechanisms involved in the growth of CdTe by organometallic vapor-phase epitaxy (OMVPE). A pyrolysis study of dimethylcadmium (DMCd) was conducted in an OMVPE reactor, in the temperature range 230/sup 0/-400/sup 0/C. It was found that dimethylcadmium decomposes above approximately 230/sup 0/C and the reaction is heterogeneous from 230/sup 0/ to 370/sup 0/C. CdTe growth was also studied over a range of temperature from 300/sup 0/ to 375/sup 0/C and for various reactor parameters. In all cases, the CdTe deposition rate was found to be closely related to the decomposition of dimethylcadmium. A model is presented to explain the CdTe growth at low temperatures where diethyltelluride is very stable. The growth of CdTe, using diethyltelluride and elemental cadmium, was demonstrated and supports the model. The growth rate of CdTe was studied as a function of the partial pressure of DMCd and DETe, and the results were explained in light of this growth model.

Elastic strains in CdTe‐GaAs heterostructures grown by metalorganic chemical vapor deposition

The elastic response associated with the lattice mismatch in (100)CdTe∥(100)GaAs heterostructures was investigated by performing photoluminescence measurements as a function of CdTe layer thicknesses. The heterostructures were grown by metalorganic chemical vapor deposition. Estimates of strains, stresses, and lattice constants were obtained from shifts in near‐band‐edge photoluminescence features. Biaxial compressive strains are present in CdTe layers thinner than 1 μm. The magnitudes of the strains are larger than those expected from equilibrium models and from transmission electron microscopy results. With increasing CdTe layer thicknesses above 0.1 μm biaxial tensile strains affect the GaAs surfaces.

Arsenic‐doped p‐CdTe layers grown by organometallic vapor phase epitaxy

Arsenic‐doped CdTe layers have been grown by organometallic vapor phase epitaxy in an atmospheric pressure reactor using arsine as the dopant gas. Doping levels above 2×1017 cm−3 have been reproducibly obtained for the first time in an epitaxial growth system, with a doping uniformity of ±20% over 1.5×1.5 cm. This is a much higher level of doping than usually possible in bulk growth systems. The layers were characterized by photoluminescence measurements at 12 K and by Hall measurements as a function of temperature. The ionization energy of the As acceptor was found to be about 62±4 meV from transport measurements. It was also shown that the electronic activity of the As incorporated is a function of the dimethylcadmium to diethyltelluride partial pressure ratio in the gas phase.

Transmission electron microscopy of (001) CdTe on (001) GaAs grown by metalorganic chemical vapor deposition

The nature of dislocations in (001) CdTe‐(001) GaAs heterostructures was investigated by transmission electron microscopy. The samples were grown by metalorganic chemical vapor deposition with CdTe layer thicknesses h ranging from 0.1 to 2.2 μm. The interface contains an array of misfit dislocations spaced about 31 A apart, independent of h. These dislocations do not relax all of the lattice mismatch (14.6%) in the CdTe layers with h<1 μm. Above the interfaces, surface nucleated dislocations are observed in the CdTe layers and their density depends on h. No evidence of an oxide or foreign interface layer was found in these samples.

The organometallic epitaxy of extrinsic p‐doped HgCdTe

Extrinsic p‐doped mercury cadmium telluride (MCT) layers have been grown by organometallic vapor phase epitaxy, using arsine in hydrogen as the dopant gas. Controllable doping in the range 3.5×1015–4.3×1016 was obtained when grown on GaAs with CdTe buffer layers. Consistently higher doping concentration (a factor of 2 to 4) was observed when a CdTe substrate was used. This is believed to be due to higher dislocation densities present when grown on GaAs, around which As may segregate. The cadmium fraction fell at very high flow; we believe that this is due to the prereaction of dimethylcadmium with arsine. Isothermal annealing under a Hg‐rich ambient of MCT grown on CdTe substrates did not produce significant changes in the measured doping concentration. This indicates that the acceptor level is extrinsic in nature and that arsenic behaves as a stable acceptor dopant in MCT. The activation energy of this acceptor was determined as a function of doping, and is about one‐half the value of the acceptor due to...

Growth of CdTe on GaAs by organometallic vapor phase heteroepitaxy

Organometallic vapor phase heteroepitaxy of CdTe on (100) oriented GaAs substrates is described in this letter. It is shown that high quality CdTe layers can be grown on GaAs substrates over the temperature range 350–440 °C by this process. Growth under different temperatures and reactant partial pressures is described. Conditions are outlined for obtaining optimum photoluminescence properties, with suppression of the defect level associated with the cadmium vacancy. Electron channeling data are presented to indicate that excellent epitaxy is achieved by this process. The orientation of the epitaxial layer is found to be the same as that of the substrate.

The organometallic heteroepitaxy of CdTe and HgCdTe on GaAs substrates

Heteroepitaxial films of CdTe and Hg1−xCdxTe have been grown on (100)GaAs substrates by organometallic vapor phase epitaxy. It is shown that high quality CdTe films can be grown on GaAs substrates over the temperature range from 350 to 440 °C. The effects of the reactant pressures on the growth rate of CdTe are also discussed. HgCdTe layers were grown, on GaAs substrates with a CdTe buffer layer, at 415 °C. Transport measurements made on these layers indicate that they are of high quality with a 80 K mobility of over 2×105 cm2/V s for layers of composition x≂0.2. Layers have been grown with different buffer layer thicknesses. It is shown that a CdTe buffer layer of at least 2–3 μ is necessary to fully accommodate the misfit dislocation at the CdTe–GaAs interface.

Extrinsic doped n- and p-type CdTe layers grown by organometallic vapor phase epitaxy

In this paper we report on the extrinsic n- and p-doping of CdTe layers, grown by organometallic vapor phase epitaxy. Triethylindium and arsine gas were used as n- and p-type dopants respectively, with doping levels of around 1017 cm-3 in both cases. Layers were grown on both semi-insulating CdTe and GaAs substrates. Layers grown on semi-insulating GaAs had an intervening 1–2 μm undoped CdTe layer to relieve the strain caused by the large (14.6%) lattice mismatch of the CdTe-GaAs combination. Van der Pauw measurements were made to evaluate the quality of these layers, and mobility values as high as 3600 cm2/V h- s obtained at 40 K for lightly doped n-type samples. Grown junctions, made using extrinsic doped layers, have resulted in diodes with excellent electrical characteristics.

Indium doping of n-type HgCdTe layers grown by organometallic vapor phase epitaxy

n‐type doping of mercury cadmium telluride was achieved using trimethylindium as the dopant source. The layers, grown by the alloy growth technique, were doped to ∼5×1018 cm−3. The donor concentration in these layers was found to exhibit a linear dependence on the dopant partial pressure over the carrier concentration range from 5×1016 to 3×1018 cm−3. Reasonably high electron mobility values were observed in these indium‐doped layers. Typically, layers with a Cd fraction x=0.23, doped to 3.5×1016 cm−3, exhibited a mobility value of 7.5×104 cm2/V s at 40 K. High electron mobility values, measured over the entire doping regime, suggest a high electrical activity of indium in these layers. The optically measured band edge in these indium‐doped layers was observed to shift to higher energy with increasing doping. The band‐edge energy values measured in 1×1017 and 3×1018 cm−3 doped layers correspond to x=0.23 and x=0.3, respectively. This increase can be due to an increase in the Cd fraction, or to a Burstein–...

Growth and properties of Hg1−xCdxTe on GaAs substrates by organometallic vapor-phase epitaxy

Growth of epitaxial mercury cadmium telluride (Hg1−xCdxTe) on (100) GaAs substrates by organometallic vapor‐phase epitaxy is described. Transport measurements made on these layers at 80 K indicate an electron mobility greater than 2×105 cm2/ V s for layers of composition x≂0.2. An intervening CdTe buffer layer was used to accommodate the large (14%) lattice mismatch between these systems, and HgCdTe layers have been grown with CdTe buffer layer thicknesses from 1000 A to 3 μm. It is shown that a CdTe buffer layer of 2–3 μm is necessary to accommodate the misfit dislocations at the CdTe‐GaAs interface.